Gas lift method



July 6, 19 5 .1. H. MOCARVELL ETAL 3,192,369

GAS LIFT METHOD Filed Oct. 28, 1963 INVENTORS ATTORNEY United States Patent This invention relates to new and useful improvements in gas lift methods for producing oil and the like from Wells.

Fluid operated valves for gas lifting oil in wells are commonly used today, as exemplified by the fluid operated valves disclosed in United States Patent Nos. 2,610,644 and 2,869,568, in which the present applicants were the inventors. Heretofore, such valves have been used to eject gas in slugs when the oil or other liquid in the tubing reached a sufficient head to open the valve. In order to lift the oil by such slugging of the gas, the pressure of the gas used for the gas lift necessarily had to be extremely high which has resulted in several problems'at the surface of the well. First, the lifting gas normally is obtained from a gas well or a compressor station atfairly high pressures. Such gas has previously been injected into the casing continuously and has been ejected at the surface in slugs of large volumes so that it has been necessary to reduce the gas pressure for storage at the surface. Normally, the gas is thereafter compressed again for injection into the well, thereby requiring horsepower to get the gas back to the pressure at which it was received from the gas well or compressor station.

Further, with the prior art procedures, the intermittent slugging of the oil with the ejected gas often resulted in periodically overloading the surface equipment with the oil and the excess gas following after the oil.

It is an object of this invention to provide a new and improved gas lift method which overcomes the aforesaid problems of the prior art gas lift procedures.

An important object of this invention is to provide a new and improved gas lift method wherein gas is con-' tinuously injected into a column of oil through a fluid operated valve to reduce the density of the column of oil and thereby obtain continuous production of the oil at the surface without a slugging of the oil with large ejected slugs of the gas.

Another object of this invention is to provide a new and improved method for producing oil from a well formation which is incapable of flowing the oil to the surfaceby its own bottom hole pressure, wherein gas is injected continuously to maintain a predetermined pressure gradient in the gas liquid mixture for producing oil continuously at the surface of the Well. V

A particular object of this invention is to provide a new and improved gas lift method wherein a plurality of longitudinally spaced gas lift valves, each' of which is adapted to be actuated by the fluid head in the tubing, is provided and wherein each valve has been set for opening at the same pressure gradient so that the quantity of the oil produced may be controlled by regulating the pressure of the lifting gas. a

A further object of this invention is to provide a new and improved method for controlling the production of oil in a well by gas lifting same so that a minimum amount of gas is used to produce the desired amount of oil.

The preferred embodiment of this invention will be described hereinafter together with other features thereof, and additional objects will become evident from such description. V

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof 3,192,869 Patented July 6, 1965 wherein an example of the invention is shown, and wherein:

FIG. 1 is a schematic illustration, partly in elevation and partly in section, illustrating a typical arrangement for carrying out the method of this invention; and

FIG. 2 is a view, partly in section and partly in elevation, illustrating a portion of the tubing string and one of the gas lift valves therewith in detail, which construction is merely an example of one type of fluid-actuated gas lift valve usable in carrying out the method of this invention.

In the drawings, the letter T designates generally a tubing string which is positioned in a casing or well pipe W for producing oil or other liquid from a formation indicated at F. As is customary, the formation F a is packed off by a well packer P disposed between the tubing string T and the casing W so that the oil or other well'fluid flows upwardly into the tubing string T. The method of the present invention is used with a well formation F in which the bottom hole pressure is insufficient to force the oil or other fluid through the discharge opening 10 at the surface of the well without pumping or gas lift. In carrying out the method ofthis invention, one or more valves V through V3 of the fluid-actuated type are employed with the tubing string T. -As will be explained more in detail hereinafter, gas is introduced into the annulus between the tubing string T and the casing W through an inlet 12 to provide gas at a predetermined pressure for maintaining a predetermined pressure gradient of the combined gas and liquid in the tubing string, whereby a sufliciently light density mixture is obtained at all times for producing oil continuously at the surface through the discharge pipe 16.

Considering the invention more in detail, FIG. 1 illustrates a typical arrangement for carrying out the method of this invention. As illustrated therein, valves V, V1,f

V-2 and V3 are illustrated as mounted on the tubing string T. Each of the valves V is preferably identical and therefore details of the valve V only have been illustrated in FIG. 2. It will be understood that the method of this invention isnot limited to the particular detailed type of valve illustrated in the drawings since any fluidactuated valve which is operated by the head of fluid in the tubing string may be employed.

Referring now to FIG. 2, it can be seen that the valve V is positioned in a suitable housing or holder 16 which is welded or otherwise secured to the tubing string T. The tubing string T has arr-opening 14 adjacent each of the valves, with such openings 14 being aligned with corresponding openings 16a in the housings or holders 16.

As particularly shown in FIG. 2, the gas lift valve V includes a valve casing 21 having a valve seat 21a at the lower end thereof. A plurality of fluid passages 21b are provided for communication directly with the interior of the tubing T through the openings 14 and 16a. The number of the openings 2117 may of course be varied and in some cases a'single opening 21b may be used. A valve stem 22 is mounted in the valve casing 21 and is urged towards a seated position by a spring 23. The spring 23 is preferably confined between a shoulder 24 and an adjustable nut 25 so that the compression of the spring 23 may be adjusted toset the amount of liquid head required to open the valve stem 22 from its seat 21a- The upper end of the stem 22 has a dampening head 27 connected thereto with split snap rings 28 of metal or other material Inounted thereon. "The snap rings 28 engage the internal surface of the valve casing 21 and dampen the movements of the stem 22, but the split in the rings'28 permits fluid flow past such rings 28 so as to prevent a fluid lock above the rings 28. A flexible bellows or diaphragm Si! is con- 1 nected to the upper end of the head 27 and the area in- =19 ternally of the bellows 30 is preferably at atmospheric pressure. A guide sleeve and stop member 31 is connected to the head 27 within the bellows 30. A closure plug 32 is connected in the upper end of the casing 21 to close the area confined by the bellows 30.

It is preferable to include a check valve C below the gas lift valve V so as to prevent a loss of the liquid within the tubing string in the event the gas pressure externally of the tubing string drops below a predetermined pressure while the valve stem 22 is moved upwardly to an open position. The check valve Cis connected to the gas lift valve V by any suitable means such as a connecting threaded sleeve 35.

The check valve C includes a housing 40 and a valve seat 40a therein which is adapted to be engaged by the lower end of a longitudinally movable valve member 41. The valve member 4-1 has a central bore 41a which is open at its upper end and which is in communication with a lateral port or ports 41!). A spring 42 holds the valve member 41 in a seated position on the valve seat 40a. However, upon an upward movement of the valve member 41 to an open position, the spring 42 is compressed and the lluid such as gas in the casing annulus then may flow through the port 4112 and the central bore 41a to the sleeve 35 and then through the openings 2112, providing the valve stem 22 has been moved to the open position by the head of liquid in the tubing T.

In carrying out the method of this invention, the well formation must have a sufficient bottom hole pressure to force the oil or other liquid up into the tubing string T above the top valve V so as to exert a head of pressure sufficient to open such valve V. The valve V, however, is referred to herein only as a typical illustration of the method since the method will function so long as the bottom hole pressure forces the oil up into the tubing T a sufficient distance to develop a head for opening at least one of such valves V through V-3.

For the purposes of the present description, it is assumed that the head of the oil from the formation F rises in the tubing string T high enough to open the valve V to admit gas from the casing annulus into the tubing string T. Once the valve V is opened by such head of oil or other liquid in the tubing string T, the gas from the annulus then llows into the-tubing string T through the valve V and mixes with and disperses throughout the head of the oil above the open valve V to form a mixture which has a lighter density than the liquid below the valve V. The valve V is set so that it remains open so long as the pressure gradient of the oil and liquid mixture acting thereon is equal to or greaterthan a predetermined amount. For example, assuming the pressure gradient is selected at 0.2 p.s.i., the valve V is set so that it opens when. the pressure acting thereon is equal to such pressure gradient of 0.2 p.s.i. Also, the pressure of the gas which is introduced from the surface through the line 12 is regulated so that it is capable of continuously flowing into the tubing string T through the valve V to mix with the oil and maintain the pressure gradient at or above the established figure at which the valve V is adapted to open.

For example, if the pressure gradient is selected to be 0.2 psi. then with the valve V at an elevation of 2000 feet below the surface of the well, it would require a casing injection gas of 400 p.s.i. or above in order to maintain such pressure gradient.

When the gas pressure of the injection gas introduced from the surface of the line 12 is thus regulated so as to maintain the liquid density of the gas-liquid mixture above the valve V at the pressure gradient sufficient to hold the valve V open continuously, the gas from the annulus is thereby injected continuously and the slugging of the oil is prevented.

If it develops that an insuflicient volume of the liquid or oil is being produced at the surface through the discharge tube 10, additional oil or other liquid may be produced by increasing the injection gas pressure.

Thus, assuming that the valve V-l is located at an elevation of 3000 feet below the surface of the well, then with the pressure gradient of the gas liquid mixture established at 0.2 p.s.i., the pressure of the gas introduced through the line 12 is increased to 600 p.s.i. or above. At such pressure, the gas will continuously flow into the tubstring T through the valve V1 and will reach the desired gradient of 0.2 p.s.i. as a result of the gas bubbling and mixing with the oil or other liquid. Additional oil will thereby be produced as compared to the situation when the gas'was being introduced through the valve V since the head of the oil mixed with the gas is greater. Very little, if any, gas is introduced through the valve V once the valve V-l is utilized, although if zTslug of oil should accidentally be developed within the tubing string T, the head above the valve V may develop to such an extent that it again opens the valve V temporarily.

As more oil is desired at the surface of the well and depending upon the surface conditions, the valves V-2 and V-3 may be brought into action by increasing the lifting gas pressure. For example, if the valve V2 is positioned at an elevation of 4000 feet below the surface of the earth, the gas pressure would be raised to 800 p.s.i. or above for the maintaining of the 0.2 p.s.i. presure gradient in the tubing string T. If the valve V-3 is assumed to be set at an elevation of 5000 feet below the surface of the well, the pressure of the gas in the annulus would be set at 1000 p.s.i. or above in order to maintain the pressure gradient of 0.2 p.s.i;

It will be understood that other pressure gradients may be established so long as the gradient is below 0.5 p.s.i. which is the pressure gradient of salt water.

Thus, with the present invention, there is a continuous injection of the gas into the tubing string from the casing annulus to continuously form the lighter density liquid gas column above the column of oil or other liquid so that the bottom hole pressure can then force the lighter density column to the surface for discharge through the discharge pipe 10. Such discharge or production can therefore continue so long as the gas is injected into the tubing string T. Since slugging of the oil to the top of the well is avoided with the present invention, the equipment for receiving the oil at the surface may be more readily known and reduced in size, depending solely upon the amount of normal continuous production expected with the well.

Additionally, excess gas on the surface of the well is unnecessary and the gas may be used at the pressure it is received without overloading the system.

The foregoing disclosure and description of the invention is illustrative, and explanatory thereof, and various changes in the size, shape and materials as well as in the details of the illustrated construction may be made with in the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A method of gas lifting oil or other liquid in a well comprising the steps of:

(a) mounting a plurality of longitudinally spaced fluid actuated valves on a tubing string,

(b) positioning the tubing string in a well casing with an annulus therebetween,

(c) setting each of said valves to open at substantially the same pressure gradient,

(d) forming a head of liquid in the tubing string above the uppermost valve to be opened for initially opening same to establish fluid communication from the annulus to the interior of the tubing string, and

(e) continuously introducing lifting gas into the annulus and through one or more of said valves to bubble the gas into the well liquid above the valve for reducing its density sufliciently to enable the bottom hole pressure of the well to raise same for discharge at the upper end of the tubing string.

2. A method of gas lifting oil or other liquid in a well comprising the steps of:

(a) positioning a tubing string having a plurality of longitudinally spaced fluid actuated valves thereon in a well bore,

(b) setting each of said valves to open at substantially the same pressure gradient,

(c) forming a head of liquid in the tubing string above the uppermost valve to be opened for initially opening same to establish fluid communication from the well bore to the interior of the tubing string,

(d) continuously bubbling gas at a predetermined pressure from the well bore into the head of fluid above the uppermost valve for forming a gas-liquid mixture above said valve to provide a predetermined pressure gradient, and

(e) continuously flowing the well liquid upwardly to mix with the injected gas and to thereby continuously form the gas liquid mixture for effecting a lifting of the gas liquid mixture upwardly to discharge same from the upper end of the tubing string.

3. A method of gas lifting oil or other liquid in a well comprising the steps of:

(a) positioning a tubing string in a well bore wherein the tubing string has a plurality of gas lift valves thereon each of which is adapted to be opened at substantially the same pressure gradient as determined by its elevation and the pressure of gas injected into the tubing string,

(b) forming a head of liquid in the tubing string above one of the valves for opening same to establish fluid communication from the well bore to the interior of the tubing string,

(c) continuously bubbling gas at a predetermined pressure from the well bore into the head of liquid above the open valve for forming a gas liquid mixture substantially at said pressure gradient and with the gas dispersed throughout the liquid above the open valve, 7

(d) continuously flowing the well liquid upwardly to mix with the injected gas and to thereby continuously form the gas liquid mixture for effecting a lifting of the gas liquid mixture upwardly to discharge same from the upper end of the tubing string,

(e) increasing the pressure of the lifting gas in the well bore for flowing such gas into another of the valves at an elevation which is lower than said one of the valves which had previously been opened, and

(f) maintaining substantially the same pressure gradient with the increased gas pressure while mixing such gas with a greater quantity of the well liquid to thereby increase the volume of the well fluid produced at the Well surface.

4. A method of gas lifting oil or other liquid in a well comprising the steps of: a

(a) positioning a tubing string in a well bore wherein the tubing string has a plurality of gas lift valves thereon each of which is adapted to be opened at substantially the samepressure gradient as determined by its elevation and the pressure of gas injected into the tubing string,

(b) forming a head of liquid in the tubing string above one of the valves for opening same to establish fluid communication from the Well bore to the interior of the tubing string,

(c) continuously bubbling gas at .a predetermined pressure fromthe well bore into the head of liquid above the open valve for forming a gas liquid mixture substantially at said pressure gradient with the gas dispersed throughout the liquid above the open valve,

(d) continuously flowing the well liquid upwardly to a mix with the injected gas and to thereby continuously form the gas liquid mixture for elfecting a lifting of the gas liquid mixture upwardly to dischargesame from the upper end of the tubing string, and

(e) successively introducing lifting gas into the valves at the successively lower elevations from the open valve until the desired quantity of liquid is being continuously produced at the surface of the well.

5. A method of gas lifting oil or other liquid in a Well comprising the steps of:

(a) positioning a tubing string in a well bore wherein the tubing string has a plurality of gas lift valves thereon each of which is adapted to be opened at substantially the same pressure gradient as determined by its elevation and the pressure of gas injected into the tubing string,

(b) forming a head of liquid in the tubing string above one of the valves for opening same to establish fluid communication from the well bore t0 the in- 1 terior of thetubing string,

(0) continuously bubbling gas at a predetermined pressure from the Well bore into the head of liquid above the open valve for forming a gas liquid mixture with the gas dispersed throughout the liquid above the open valve,

(d) continuously flowing the well fluid upwardly to mix with the injected gas and to thereby continuously form the gas liquid mixture for effecting a lifting of the gas liquid mixture upwardly to discharge same from the upper end of the tubing string,

(e) successively introducing lifting gas into the valves at the successively lower elevations from the open valve until the desired quantity of liquid is being continuously produced at the surface of the well, and

(f) maintaining the pressure gradient in the tubing fluid the same above each valve into which the gas is introduced so that only the lowermost valve exposed to the lifting gas in the well bore is normally passing such gas therethrough.

References Cited by the Examiner UNITED STATES PATENTS 1,884,550 10/32 Boynton 103233 2,292,768 8/42 Parker 103-233 2,869,568 1/59 McCarvell et al. 137-155 2,982,226 5/61 Peters et a1 l03233 LAURENCE V. EFNER, Primary Examiner. 

1. A METHOD OF GAS LIFTING OIL OR OTHER LIQUID IN A WELL COMPRISING THE STEPS OF: (A) MOUNTING A PLURALITY OF LONGITUDINALLY SPACED FLUID ACTUATED VALVES ON A TUBING STRING, (B) POSITIONING THE TUBING STRING IN A WELL CASING WITH AN ANNULUS THEREBETWEEN, (C) SETTING EACH OF SAID VALVES TO OPEN AT SUBSTANTIALLY THE SAME PRESSURE GRADIENT, (D) FORMING A HEAD OF LIQUID IN THE TUBING STRING ABOVE THE UPPERMOST VALVE TO BE OPENED FOR INITIALLY OPENING SAME TO ESTABLISH FLUID COMMUNICATION FROM THE ANNULUS TO THE INTERIOR OF THE TUBING STRING, AND (E) CONTINUOUSLY INTRODUCING LIFTING GAS INTO THE ANNULUS AND THROUGH ONE OR MORE OF SAID VALVES TO BUBBLE THE GAS INTO THE WELL LIQUID ABOVE THE VALVE FOR REDUCING ITS DENSITY SUFFICIENTLY TO ENABLE THE BOTTOM HOLE PRESSURE OF THE WELL TO RAISE SAME FOR DISCHARGE AT THE UPPER END OF THE TUBING STRING. 